The invention relates to a process for frequency range tuning a resonant circuit of metal-plastic-metal laminate foil for an identification label or tag and a laminate foil suitable for carrying out the process.
Identification tags are employed with a single resonant circuit for example thief-proof labels, or a plurality of resonant circuits such as for example for arranging objects such as packets, cases or in certain countries in vehicles to calculate road user's taxes, in all cases for non-contact identification of objects that are not kept in a fixed place.
The production and use of the resonant circuit of metal-plastic-metal laminate foil for such identification labels or tags is in fact known from U.S. Pat. No. 3,671,721 and WO 86/02186. In order to employ resonant circuits as identification tag/tags IL is necessary that each resonant circuit causes interference within an exactly prescribed frequency range of close tolerance and, consequently, for example when used as a tag to prevent theft, actuates an optical or accoustic signal.
A resonant circuit can be made from a metal-plastic-metal laminate foil which, from the choice of material is of high quality and can be manufactured in a continuous manner. Difficulties do arise in large scale or mass production of resonant circuit structures of metal-plastic-metal laminate foils as the production parameters and in particular the thickness tolerances of the layers of laminate foil used, as well as the alterations in the foil necessary in the construction of the individual resonant circuits, have a considerable influence on the detection frequency of the finished resonant circuit.